Bit line sense amplifier control circuit

ABSTRACT

A bit line sense amplifier control circuit comprises a driving signal generating unit adapted and configured to generate first through third driving signals in response to a bit line sense amplifier enable signal and an overdrive enable signal for setting an overdrive period, and to disable a first driving signal which is enabled for an overdrive period in response to a refresh signal which is enabled at a refresh mode, and a bit line sense amplifier control signal generating unit adapted and configured to generate first and second bit line sense amplifier control signals in response to the first through third driving signals. As a result, an overdrive pulse is not generated at a refresh mode to remove an overdriving period, thereby reducing current consumption at a refresh mode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a bit line sense amplifiercontrol circuit of a semiconductor memory device, and more specifically,to a technology of removing an overdriving period at a refresh mode,thereby reducing current consumption at a self-refresh mode.

2. Description of the Related Art

Generally, a bit line sense amplifier senses and amplifies data on a bitline to output the data to a data bus, and a data bus sense amplifierre-senses and re-amplifies the data amplified by the bit line senseamplifier to output the data to a data output buffer.

The operation of the general bit line sense amplifier is described asfollows. Here, a cross coupled latch type amplifier is exemplified forthe bit line sense amplifier.

First, a bit line is precharged to a precharge voltage (for example,half of an internal power voltage VDD). Here, two bit lines areequalized to remove a voltage difference between one bit line connectedto a selected memory cell and another bit line which is not connected tothe selected memory cell.

A row decoder decodes an externally inputted row address to select aword line corresponding to the row address.

Then, a cell transistor connected to the selected word line is turnedon.

As a result, a potential difference is generated between one bit lineconnected to a selected memory cell and another bit line which is notconnected to the selected memory cell by charge sharing between cellcapacitance and bit line capacitance.

Here, when sense amplifier control signals RTO and SB are enabled, thesense amplifier control signal RTO becomes at a high level VDD, and thesense amplifier control signal SB becomes at a low level VSS. As aresult, a bit line sense amplifier is operated to amplify the potentialdifference between the bit line connected to the selected memory celland another bit line which is not connected to the selected memory cell.

For example, suppose that data stored in the selected memory cell is lowlevel data. A potential of the bit line connected to the selected memorycell becomes lower than that of a precharge voltage, and a potential ofthe bit line which is not connected to the selected memory cell ismaintained at that of the precharge voltage, so that a potentialdifference occurs between the two bit lines.

Therefore, the bit line sense amplifier which is a cross coupled latchtype amplifier sets the bit line connected to the selected memory cellat the low level VSS by the low level bit line sense amplifier controlsignal SB, and sets the bit line which is not connected to the selectedcell at the high level VDD by the high level bit line sense amplifiercontrol signal RTO.

Thereafter, a column address is decoded by a column decoder. When acolumn control signal YI corresponding to the column address is enabledto a high level, data on the bit line is amplified by the bit line senseamplifier and transmitted into a data bus.

The control signal RTO for driving the bit line sense amplifier isdriven as an external power voltage VEXT at the initial amplificationoperation in order to improve an operating speed of the bit line senseamplifier, thereby reducing a skew. At a normal mode, the control signalRTO is driven to an internal power voltage (core voltage) VCORE or aninternal circuit supply voltage VPERI.

In case of a low power semiconductor memory device, a method forreducing current consumption is more preferably used than a method forimproving an operating speed at a self-refresh mode. However, thecurrent consumption is increased because the bit line sense amplifiercontrol signal RTO is driven to the external power voltage VEXT higherthan the internal power voltage VCORE which is a target voltage for anoverdriving period.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to remove anoverdriving period at a refresh mode, thereby reducing currentconsumption.

According to one embodiment of the present invention, a bit line senseamplifier control circuit comprises a driving signal generating unitadapted and configured to generate first through third driving signalsin response to a bit line sense amplifier enable signal and an overdriveenable signal for setting an overdrive period and to disable the firstdriving signal which is enabled for an overdrive period in response to arefresh signal which is enabled at a refresh mode, and a bit line senseamplifier control signal generating unit adapted and configured togenerate a first bit line sense amplifier control signal and a secondbit line sense amplifier control signal in response to the first throughthird driving signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects and advantages of the present invention will becomeapparent upon reading the following detailed description and uponreference to the drawings in which:

FIG. 1 is a block diagram illustrating a bit line sense amplifiercontrol circuit according to an embodiment of the present invention;

FIG. 2 is a circuit diagram illustrating a driving signal generatingunit of FIG. 1;

FIG. 3 is a circuit diagram illustrating a bit line sense amplifiercontrol signal generating unit of FIG. 1; and

FIGS. 4 and 5 are timing diagrams illustrating the operation of the bitline sense amplifier control circuit of FIG. 1.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention will be described in detail with reference to theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

FIG. 1 is a block diagram illustrating a bit line sense amplifiercontrol circuit according to an embodiment of the present invention.

In this embodiment, a bit line sense amplifier control circuit comprisesa driving signal generating unit 10 and a bit line sense amplifiercontrol signal generating unit 20.

The driving signal generating unit 10 generates driving signals SAP1 andSAP2 for driving a bit line sense amplifier control signal RTO and adriving signal SAN for driving a bit line sense amplifier control signalSB in response to a sense amplifier enable signal SAENB, an overdriveenable signal SAElB having a pulse width to determine an overdrivingperiod and a self-refresh signal SELFREF.

The bit line sense amplifier control signal generating unit 20 generatesbit line sense amplifier control signals RTO and SB in response to thedriving signals SAN, SAP1 and SAP2 and a bit line equalizing signalBLEQ.

FIG. 2 is a circuit diagram illustrating the driving signal generatingunit 10 of FIG. 1.

The driving signal generating unit 10 comprises inverters IV1˜IV7, andNAND gates ND1 and ND2.

The inverters IV1, IV2 and IV3 sequentially invert the bit line senseamplifier enable signal SAENB to generate the low level driving signalSAN.

The NAND gate ND1 performs a NAND operation on an output signal from theinverter IV1 and the overdrive enable signal SAElB. The inverter IV4inverts an output signal from the NAND gate ND1 to generate the secondhigh level driving signal SAP2.

The inverter IV5 inverts the overdrive enable signal SAE1B, and theinverter IV6 inverts the self-refresh signal SELFREF. The NAND gate ND2performs a NAND operation on output signals from the inverters IV5 andIV6. The inverter IV7 inverts an output signal from the NAND gate ND2 togenerate the first high level driving signal SAP1. As a result, aself-refresh mode is entered, and the first high level driving signalSAP1 is maintained at a low level when the self-refresh signal SELFREFis enabled to a high level, so that an overdrive operation is notperformed.

FIG. 3 is a circuit diagram illustrating the bit line sense amplifiercontrol signal generating unit 20 of FIG. 1.

The bit line sense amplifier control signal generating unit 20 comprisesa high level bit line sense amplifier control signal driving unit 21, alow level bit line sense amplifier control signal driving unit 22 and anequalizing unit 23.

The high level bit line sense amplifier control signal driving unit 21comprises PMOS transistors PT1 and PT2. The PMOS transistor PT1 drivesthe high level bit line sense amplifier control signal RTO to anexternal power voltage VEXT in response to the first high level drivingsignal SAP1B, and the PMOS transistor PT2 drives the high level bit linesense amplifier control signal RTO to a core voltage VCORE in responseto the second high level driving signal SAP2B.

The low level bit line sense amplifier control signal driving unit 22comprises a NMOS transistor NT1 which drives the low level bit linesense amplifier control signal SB to a ground voltage VSS in response toa low level driving signal SAN.

The equalizing unit 23 comprises NMOS transistors NT2, NT3 and NT4. TheNMOS transistors NT2 and NT3 precharge the bit line sense amplifiercontrol signals.RTO and SB to a bit line precharge voltage VBLP inresponse to the bit line equalizing signal BLEQ. The NMOS transistor NT4equalizes the bit line sense amplifier control signals RTO and SB inresponse to the bit line equalizing signal BLEQ.

FIG. 4 is a timing diagram illustrating the operation of the bit linesense amplifier control circuit of FIG. 1. Here, FIG. 4 shows when anoverdriving period is included at a normal mode.

While the first high level driving signal SAP1 is at a high level, thePMOS transistor PT1 of the high level bit line sense amplifier controlsignal driving unit 21 is turned on, so that the high level bit linesense amplifier control signal RTO is driven to the external powervoltage VEXT. As a result, a potential of the bit line BL having celldata is rapidly increased.

Thereafter, the first high level driving signal SAP1 becomes at a lowlevel, and the second high level driving signal SAP2 becomes at a highlevel. The PMOS transistor PT1 of the high level bit line senseamplifier control signal driving unit 21 is turned off, and the PMOStransistor PT2 is turned on. As a result, the high level bit line senseamplifier control signal RTO is driven to the core voltage VCORE, sothat the potential of the bit line BL having the cell data is maintainedat the core voltage VCORE.

FIG. 5 is a timing diagram illustrating the operation of the bit linesense amplifier control circuit of FIG. 1. Here, FIG. 5 shows when anoverdriving period is not included at a self-refresh mode.

The first high level driving signal SAP1 is maintained at the low level,and the second high level driving signal SAP2 becomes at the high level.The PMOS transistor PT1 of the high level bit line sense amplifiercontrol signal driving unit 21 is turned off, and the PMOS transistorPT2 is turned on. As a result, the high level bit line sense amplifiercontrol signal RTO is driven to the core voltage VCORE, so that apotential of the bit line BL having the cell data is maintained at thecore voltage VCORE.

As described above, in a bit line sense amplifier control circuitaccording to an embodiment of the present invention, an overdrivingperiod is removed at a refresh mode to reduce refresh current.

The foregoing description of various embodiments of the invention hasbeen presented for purposes of illustrating and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention. Thus,the embodiments were chosen and described in order to explain theprinciples of the invention and its practical application to enable oneskilled in the art to utilize the invention in various embodiments andwith various modifications as are suited to the particular usecontemplated.

1. A bit line sense amplifier control circuit comprising: a drivingsignal generating unit adapted and configured to generate a plurality ofdriving signals in response to a bit line sense amplifier enable signaland an overdrive enable signal, wherein the plurality of driving signalsincludes at least one overdrive driving signals for setting an overdriveperiod, wherein the overdrive driving signals are disabled when arefresh signal is enabled; and a bit line sense amplifier control signalgenerating unit adapted and configured to generate a first bit linesense amplifier control signal and a second bit line sense amplifiercontrol signal in response to the plurality of driving signals.
 2. Thebit line sense amplifier control circuit according to claim 1, whereinthe driving signal generating unit comprises: a first combination unitadapted and configured to generate the overdrive driving signals inresponse to the overdrive enable signal and to be disabled the overdrivedriving signals when the refresh signal is enabled; and a secondcombination unit adapted and configured to generate the rest of thedriving signals in response to the bit line sense amplifier enablesignal.
 3. The bit line sense amplifier control circuit according toclaim 2, wherein the first combination unit comprises a first logic unitadapted and configured to maintain the overdrive driving signals at apredetermined level regardless of the overdrive enable signal while therefresh signal is enabled.
 4. The bit line sense amplifier controlcircuit according to claim 2, wherein the second combination unitcomprises: a second logic unit adapted and configured to be enabled oneof the rest of the driving signals when the bit line sense amplifierenable signal is enabled; and a third logic unit adapted and configuredto be enabled other of the rest of the driving signal when the bit linesense amplifier enable signal is enabled and the overdrive enable signalis disabled.
 5. The bit line sense amplifier control circuit accordingto claim 4, wherein the third logic unit includes an AND gate.
 6. Thebit line sense amplifier control circuit according to claim 2, whereinthe bit line sense amplifier control signal generating unit comprises: afirst driving unit adapted and configured to drive the first bit linesense amplifier control signal to a high level in response to theoverdrive driving signal and the one of the rest of the second drivingsignals; and a second driving unit adapted and configured to drive thesecond bit line sense amplifier control signal to a low level inresponse to the other of the rest of the driving signals.
 7. The bitline sense amplifier control circuit according to claim 6, wherein thebit line sense amplifier control signal generating unit furthercomprises a precharge unit adapted and configured to precharge andequalize the first bit line sense amplifier control signal and thesecond bit line sense amplifier control signal in response to a bit lineequalizing signal.
 8. The bit line sense amplifier control circuitaccording to claim 6, wherein the first driving unit comprises: a firstdriving means adapted and configured to drive the first bit line senseamplifier control signal to a target voltage in response to the one ofthe rest of the driving signals; and a second driving means adapted andconfigured to drive the first bit line sense amplifier control signal toa first power voltage higher than the target voltage in response to theoverdrive driving signal.
 9. The bit line sense amplifier controlcircuit according to claim 8, wherein the target voltage is selectedfrom a core voltage and internal power voltages used in an internalcircuit.
 10. The bit line sense amplifier control circuit according toclaim 8, wherein the first power voltage is an externally appliedexternal power voltage.
 11. The bit line sense amplifier control circuitaccording to claim 6, wherein the second driving unit comprises a thirddriving means adapted and configured to drive the second bit line senseamplifier control signal to a second power voltage which is a low levelin response to the other of the rest of the driving signals.
 12. The bitline sense amplifier control circuit according to claim 11, wherein thesecond power voltage is a ground voltage.